In a construction field, an automobile field and the like, double glazing has been heretofore used for the purpose of heat insulation, dew condensation prevention, sound insulation and the like. As such double glazing, there is known double glazing having glass plates, a spacer placed between the peripheries of the glass plates and an airtightly sealed air space formed between the glass plates, the spacer being formed of rubber, resin or the like having a drying agent mixed therein, the airtightly sealed air space being shut out from ambient air (see Japanese patent application Kokai publication Nos. 10 (1998)-110072 and 2001-354949, for example).
When double glazing as described above is manufactured, the following two methods of forming a spacer have been well known (see Japanese patent application Kokai publication Nos. 8 (1996)-67537 and 10 (1998)-511072, for example). One is a method of forming a spacer by extruding a spacer forming material along and between the peripheries of two glass plates held with a predetermined space therebetween. The other is a method of forming a spacer by extruding a spacer forming material along the periphery of the upper surface of one glass plate before the other glass plate is press-attached thereon.
In the latter method, a multi-joint robot having an applicator head for applying a spacer forming material is used, and while the applicator head is being moved by the multi-joint robot along the periphery of the upper surface of one glass plate which is horizontally held, the spacer forming material is applied at a constant application amount to automatically form the spacer. When the applicator head reaches each corner of the glass plate, the multi-joint robot rotates the applicator head to change the direction of the discharge port of the applicator head that discharges the spacer forming material.
Recently, due to the intensifying competition among companies, reduction in costs of double glazing has been demanded. Therefore, in the foregoing method using the multi-joint robot, if productivity is improved by increasing the movement speed (60 mm/sec. or more) of the applicator head to reduce costs, a large amount of spacer forming material runs off a predetermined application area outward in each corner region of the glass plate, thereby deteriorating the appearance of the spacer that has been formed. This is because it is structurally impossible to make the rotation speed of the applicator head follow the increased movement speed of the applicator head.
Consequently, in the process of automatically forming a spacer by use of a multi-joint robot, the applicator head is moved along the periphery at a constant speed in accordance with the rotation speed of the applicator head in order to obtain a good spacer shape. Thus, the movement speed of the applicator head, that is, the speed of forming a spacer has to depend on the rotation speed of the applicator head, which hinders improvement in productivity.